[Risk of radiation-related cancer following exposure to diagnostic radiation].

The paper on the risk of radiation-related cancer following exposure to diagnostic X-ray, appeared in the issue of Jan 31, 2004 of the Lancet, and described an attributable risk estimate of 3.2% from the current medical exposure among the cancer incidences in Japan. While the fact that Japan is known as a country with the highest level of medical exposure, the quantification of radiation-related cancer risk have made quite an impact on medical society. The risk estimate based on the linear-non-threshold (LNT) dose response that remains unresolved scientifically need further research, but the radiation risk has been a useful tool not only for decision-making by risk-benefit analysis such as justification of medical use of radiation, but also for comparison with other risks. Recent radiation biology suggests that a bystander effect and adaptive response might modify the estimated cancer risk based on the LNT model at low doses. The risk from most diagnostic X-rays may be so small that excess cancer due to radiation can not be statistically detected. However, a diagnosis giving a relatively higher dose such as computer tomography in children should be carefully justified using a risk estimate. Raising awareness of low-dose cancer risk should involve not only understanding the process of risk estimation including data and assumption but also understanding there is indirect evidence for risk of lower level radiation exposure in medical procedures.